74 TILLERS OF THE GROUND 



CHAP. 



find that a plant or an animal which does not grow 

 naturally in a country, multiplies so fast when 

 brought there by man, that it displaces native 

 plants and animals. 



FIG. 18. Prickly Pear, Dordrecht, South Africa, showing how the 

 plant has run wild. 



When this occurs something else frequently 

 happens also. We sometimes find that the intro- 

 duced plant or animal, in the course of its rapid 

 multiplication, shows all sorts of differences from 

 the original plants and animals. As we say, it runs 

 into many varieties. The original prickly pears. 



